Field of the Invention
The present invention relates to a telescopic mast comprising a plurality of telescopic sections each with walls extending in the longitudinal direction of the mast, where the transverse dimension of the innermost telescopic section is smaller than the outermost telescopic section of two adjacent telescopic sections, so that the innermost telescopic section can slide longitudinally in and out of the outermost telescopic section of two adjacent telescopic sections wherein a restrictor is provided between two adjacent telescopic sections, the restrictor comprising a longitudinally extending linear guide means provided on one of two adjacent telescopic sections and a clamping means provided on the other one of two adjacent telescopic sections, wherein the clamping means is configured for providing a clamping force to the guide means during relative movement of said two adjacent telescopic sections, wherein the clamping force include two opposite directed rotation force components in a plane normal to the longitudinal direction of the mast and perpendicular to the radius of the mast through the guide means.
Furthermore the present invention relates to a restrictor for a telescopic mast.
Description of Related Art
Telescopic masts have been employed in various applications. The mast comprises a plurality of sections that decrease in size, such that the sections can be arranged coaxially inside each other.
The telescopic mast can be extended in its longitudinal direction from a collapsed state to an extended state. In the collapsed state the length of the mast corresponds to that of the longest section. Most commonly the sections have the same length. In its extended state the sections become narrower from its base towards the head of the mast. The height of the mast in its extended state is less than the sum of the length of the sections, because each section overlaps to provide stability and resistance to bending forces and wind forces on the mast.
The head provides a platform for various types of equipment, for example, surveillance equipment, reconnaissance equipment, target tracking equipment or communication equipment. Such equipment may for example, comprise cameras, sensors or aerials.
A special problem of telescopic masts is that of play due to tolerances between adjacent sections. As play occurs between all adjacent sections the play will accumulate from the base of the mast to the head and thus the platform. This is especially pronounced with tall masts comprising many sections. Play between the sections will allow relative movement of the platform in relation to the base of the mast.
The term “play” in the present application is defined as an unintended sudden and unpredictable movement of one section relative to another section.
In mobile applications, for example, on a vehicle, the mast is subject to accelerations in various directions as the vehicle moves. These accelerations will force the platform to move in relation to the base due to the play between the sections. When the vehicle is stationary, the play may still be a factor because as the sensors move they apply a force to the mast due to inertia.
An angular play of the mast in rotation of a very small magnitude results in very large inaccuracies at a distance of several kilometers. Such inaccuracy is unacceptable for the above mentioned types of equipment and especially for target tracking equipment.
Bending of the mast also gives rise to play in the form of relative movement of the platform in relation to the base of the mast and as a consequence an unacceptable inaccuracy in the vertical direction at the distances at which the equipment is required to point at and follow an object.
In mobile systems, advanced cameras and sensors equipped with gyros are able to compensate for the movements of the platform as the vehicle moves along a rough or inclined surface. The movements of the platform due to the vehicle movements are relatively slow and gradual. However, the movements of the platform due to play are sudden and, as the sections reach the limit of movement, gives rise to an impact in a given direction. The impact cause an acceleration spike that is applied to the equipment through the platform. Such acceleration spikes are very difficult to compensate for and therefore the sensor systems may fail to provide the required capability.
Systems to minimize or eliminate play have therefore been proposed in the past to solve this problem.
German Application DE 10019576 A1 describes a telescopic device with telescoping tubes. On a guide element a number of rollers are provided, for applying a set force to the tubes perpendicular to the direction of movement of the telescoping tubes. The purpose of the rollers is to minimize play of the telescoping tubes. This device is not suited for applications where the components are subject to dust and sand particles because accompanying wear of the rollers and tube surfaces will reduce the force applied by the rollers.
In International Patent Application publication WO 2008/028490 A1 and corresponding, commonly owned U.S. Pat. No. 8,695,286, an example of such a system has been proposed. A telescopic mast is disclosed with a system to minimize play between the telescoping sections. Although successfully employed this system is complex.